Why wasn’t this question done?

They should be different, because for tower structures, seismic forces act in both horizontal and vertical directions, and the seismic forces in these two directions are not identical. The two directions for the spherical tank are the same; therefore, the forces acting on the spherical tank are greater than those on the tower.

Your explanation isn’t quite correct; there is only one seismic force specified in the standards for spherical tanks.

This post was last edited by Zhanxia on 2021-5-26 at 14:16. The greater the stiffness of the structure, the shorter its period, and the greater the seismic forces it experiences.

The original poster should take a look at GB/T50761; I certainly didn’t understand it.

Towers are multi-point systems, so seismic forces are calculated segment by segment; spherical tanks consist of a single point, with all their mass considered together, which is why spherical tanks are larger in size

The natural vibration period of a structure is T=√(m/k); the greater the stiffness, the larger the denominator, and thus the smaller the period. This is the answer to the first question: the greater the stiffness, the shorter the period. The relationship between period and seismic force is determined based on the seismic response spectrum; it mainly involves a comparison between the structure’s natural vibration period and the site-specific period. China’s seismic code defines three phases. Assuming that the site-specific period remains constant, then: ① in the rising phase, the shorter the natural vibration period, the smaller the seismic force (period range: 0–0.1 s); ② in the horizontal phase, the natural vibration period has no effect on seismic force (period range: 0.1–Tg); ③ in the falling phase, the shorter the natural vibration period, the greater the seismic force (period > Tg). This figure is in the resistance code. The relationship between most structures and sites is such that the natural vibration period of the structure is greater than the characteristic period; hence it falls within the descending range. Therefore, the shorter the structural period, the greater the seismic force – this is the answer to the second question. In summary, in the vast majority of cases, the greater the stiffness of a structure, the shorter its period, and the greater the seismic forces it experiences. This is what I found regarding structures; please check if it is correct. The question now is: must the natural vibration period always lie in the decreasing phase? I also did a rough calculation using SW6, making sure that the H/D ratio and mass of the towers were similar. The seismic forces calculated were indeed higher for the spherical tanks, but their natural vibration periods were not in the decreasing range; this is probably due to their shape (the spherical tanks are off-the-shelf products). Additionally, as mentioned above, the seismic force on the tower is segmented, so it is small. One cannot definitely compare a single section to the entire spherical tank here.

This post was last edited by wanlirn on 2021-5-27 at 12:50. Formula for calculating seismic force: Seismic force = Self-weight × Seismic coefficient. The seismic coefficient is the ratio of the maximum ground acceleration during an earthquake to the acceleration due to gravity; it is expressed in units of K and serves as a quantitative indicator for determining the intensity of an earthquake. Which one do you say we should choose? I think the purpose of posing this question is to highlight the fact that people tend to focus on tall and slender towers, considering them to be more prone to danger during earthquakes; it serves as a reminder to designers that spherical tanks, which are shorter and rounder in shape, also need to have earthquake risks taken into account

It’s obvious that the questions were created by a professor. Is it meaningful to compare projects? But it did indeed help you deepen your understanding of the formulas:lol:lol:lol